UNANESTHF.TIZEl) POIKILOTHERMIC DOG— KELLER 69 



Dog 447 and Dog 442 were both completely poikilothermic according to the cri- 

 terion of cooiing to 28° C. in three hours. Note that the lines fitted through the 

 heat production points for the 2 animals both show a progressive straight line fall 

 but that the slope of the curve for 447 is steeper than the one for 442 ; 447 having a 

 calculated Qio of 2.8 and 442 one of 2.5. This difference in Qio seemingly is due 

 to the fact that 447's basal heat production was in the normal range, whereas 442 

 suffered a 20 per cent reduction and at lower body temperatures the spread betzueen 

 the heat production values progressively decreased. ( It also follows that the elevated 

 basal energy metabolism mediated by the endocrine hypothalamus is maximally 

 effective only at the homotherm temperature level.) Thus, one can roughly predict 

 that the Qio for a completely poikilothermic dog with an associated maximal reduc- 

 tion in basal heat will be in the neighborhood of 2.2. Accordingly, in using the O,,;. 

 as a criterion for evidencing the absence of or the retention of a non-shivering cold 

 stimulated internal heat source it is necessary to take into account the presence and 

 magnitude of any associated reduction in basal energy metabolism. 



Cold stimulated non-shivering heat production. The cooling curve on the 

 other 2 dogs in figure 6 reflects the retention of remnantal non-shivering cold stimu- 

 lated heat production. In Dog 350 it took an extra hour and in Dog 380 an extra 

 four hours to cool to 28° C. The calculated Qto was 2.1 for 350 and 1.6 for 380. 

 Both figures correlate well with the degree of retained heat-producing ability indi- 

 cated by the cooling curves. 



Other examples of close correlations between cooling curves and calculated heat 

 production values at different body temperatures are illustrated in figures 7 and 8 by 

 Dogs 396 and 2)2>7 . In Dog 396 the body cooled during the first hour at the rate of a 

 completely poikilothermic animal after which the curve moved decidedly to the right. 

 Similarly, heat production at a core temperature of 35° C. indicated a fall in heat 

 production at the rate of a Qio in the same range of that for the non-heat regulating 

 animal but subsequently plateaued such that there was as much heat being produced 

 at a core temperature of 30° C. as there was at Z2)° C. This demonstrates the pres- 

 ence of a sizeable remnant of non-shivering heat producing ability which was acti- 

 vated at a considerably increased threshold. Further, the amount of heat produced 

 was progressively increased as body temperature was lowered (see also heat pro- 

 duction points for Dog 380 in figure 6). In spite of a maximal reduction in basal 

 oxygen consumption Dog ?)2)7 exhibited both non-shivering and shivering heat pro- 

 ducing ability, exhibiting a Qio in the neighborhood of 1.6 for heat production up 

 to the time when shivering was activated. 



The subject of cold-stimulated non-shivering heat production requires further 

 comment. There has long been a controversy as to whether there is an automatic 

 increase in non-shivering heat production in response to cold. Analysis of the fore- 

 going data should leave no doubt as to the existence of a non-shivering heat source 

 in the dog. It should he emphasised that cold-stimulated, non-shivering heat pro- 

 duction is just as distinct an entity as is shivering heat production. Each has sepa- 

 rate and distinct nerve cell and descending fiber tract representation in the hypo- 

 thalamic gray matter and brain stem. Each is equally dependent upon nerve impulses 

 efferenting from these neurons. Following hypothalamic ablations remnants of each 

 may be disassociated one from the other and may exhibit a markedly increased 



